1. Field of the Invention
The present invention relates to a mechanical oil pressure control apparatus for an antilock brake system applied to vehicles.
2. Description of the Prior Art
Car accidents are mainly caused by over-speed and inefficient braking. Even in the running of a vehicle at a normal speed, an increase in the occurrence of accidents may occur under the condition in which the braking distance of the vehicle increases. In particular, when a vehicle is braked on a snowy or rainy road, its center of gravity may be laterally shifted, thereby causing the vehicle to be rotated. Thus, the steering function of the vehicle may be lost. In such a case, a terrible accident may occur.
In order to solve such a problem, antilock brake systems have conventionally been used. Such antilock brake systems are configured to repeatedly conduct a braking operation and a brake releasing operation within a short period of time when a brake pedal is depressed, thereby reducing a vehicle rotation phenomenon caused by a lateral shift of the vehicle""s gravity center while reducing the braking distance. However, all known antilock brake systems are insufficient to reduce the vehicle rotation phenomenon and the braking distance to a desired range. Furthermore, in known antilock brake systems, vibrations is transmitted to the brake pedal during the procedure of repeatedly conduct a braking operation and a brake releasing operation, thereby causing the driver to be confused. In particular, conventional antilock brake systems cannot be applied to a motorcycle having two wheels because it cannot exhibit its antilock braking effect in that the motorcycle has structural characteristics causing the motorcycle to easily lose its balance even by a slip occurring for a very short period of time.
As a result of experiments, the inventor found that a maximum braking effect is obtained when the wheels of a vehicle are braked while conducting a rolling friction against the ground in the vicinity of the point of time corresponding to a brake lock point, without conducting a slipping friction against the ground, that is, at a slippage rate of less than 0.2. In accordance with this principle, the inventor has made a technique for maintaining the hydraulic pressure, applied to the brake device when the driver depresses the brake pedal or pulls the brake lever, to a level in the vicinity of a brake lock point calculated taking into consideration the weight and average running speed of the vehicle.
Therefore, an object of the invention is to provide a mechanical oil pressure control apparatus for an antilock brake system of a vehicle capable of minimizing the braking distance of the vehicle while maintaining a stable steering function and exhibiting a rapid response of oil pressure to a braking operation, thereby achieving an improved stable braking effect while preventing vibrations from being transmitted to a brake pedal of the vehicle and preventing the steering function from being lost due to a lateral shift of the vehicle""s gravity center when the vehicle is braked while running on a snowy or rainy road.
In accordance with the present invention, this object is accomplished by providing a mechanical oil pressure control apparatus for an antilock brake system of a vehicle arranged between a master cylinder and a wheel cylinder both included in the antilock brake system and adapted to control an oil pressure transmitted from the master cylinder to the wheel cylinder comprising: a first body defined with a recess therein, the first body also having an oil inlet passage communicating with the master cylinder and an oil outlet passage communicating with the wheel cylinder; a hollow second body threadedly coupled to a front end of the first body; a cylinder member sealably inserted into the recess of the first body to define an oil chamber communicating with the oil inlet and outlet passages of the first body; a piston slidably fitted in the cylinder member while being subjected to an oil pressure supplied from the master cylinder and exerted in the oil chamber in such a fashion that a front end thereof slides axially in the oil chamber between a front position where the oil chamber is allowed to communicate with both the oil inlet and outlet passages and a rear position where the communication of the oil chamber with the oil outlet passage is cut off; and means for always urging the piston to move toward the front position against the oil pressure exerted in the oil chamber, the urging force of the urging means being adjusted in such a fashion that the oil pressure established at the point of time when the piston reaches the rear position substantially corresponds to a brake lock point of the antilock brake system.